A booster amplifier is used to amplify wireless communication signals. More particular, a signal booster is a device that automatically receives, amplifies, and retransmits on a bidirectional or unidirectional basis, the signals received from base, fixed, mobile, or portable stations, with no change in frequency or authorized bandwidth.
Such signals boosters are used in transport vehicles like cars, trains and so on. However, the use of signal boosters is not limited to transport vehicles. They can also be used within buildings for example. Signal boosters comprise a first antenna and a second antenna, wherein the first antenna is arranged within the transport vehicle and wherein the second antenna is arranged at the outside of the transport vehicle. The first antenna is used for sending and receiving communication signals to and from a mobile, wherein the second antenna is used for sending and receiving communication signals to and from a base station. Thus, the mobile is connected to the base station through the signal booster. It is very advantageous that the transmit power of the mobile is far below of its maximum transmit power, whereby it is still ensured at the same time that a stable connection is established between the mobile and the base station. This connection is independent of any influence from an electromagnetic shielding the transport vehicle may comprise.
In general, a repeater is also some kind of signal booster. However, a repeater is able to amplify a signal with a much higher gain than a signal booster.
Unfortunately, it is possible that the use of a signal booster disrupts cellular systems. This disruption may not be limited to the network the signal booster uses, but could also be spread to other neighboring networks. A power overload situation may occur. In a result, other devices may be disconnected. A signal booster may also increase the noise floor, which decreases the sensitivity of the base station and therefore reduces the covered area for all devices. This could also result in a poor reception by the base station inhibiting a mobile to establish a communication at all.
Among the provisions to prevent these malfunctions too much noise should be avoided. In order to obtain an approval for operating a booster device, the FCC (Federal Communication Commission) has issued guidelines that any booster device has to comply with. Reference is made to FCC Title 47, Chapter I, Subchapter B, Part 20, § 20,21 (Signal boosters) dated Feb. 11, 2015 which is herein incorporated by reference.
The FCC demands that a signal booster device has to meet the noise and gain limits. Otherwise it must operate in a “Transmit Power Off Mode” in which at least the uplink amplifier is deactivated (i.e. powered off). In that case, the uplink amplifier has an attenuation of more than 30 dB. If the signal booster device is installed in a vehicle the attenuation based on materials used in the bodywork of the vehicle is high but normally less than 30 dB. As such, the mobile therefore communicates directly with the base station.
Therefore, the problem addressed herein is that of describing and/or creating a signal booster device and a method for fulfilling the FCC requirements with respect to signal boosters in a reliable and repeatable manner, wherein a stable communication link should still be provided even if the signal booster device cannot be operated in normal operation mode due to too much noise.